Re: the P2M/VP patch merge plan (was Re: [Xen-ia64-devel] [PATCH][RFC][TAKE5] the P2M/VP patches)

[Tristan Gingold <Tristan.Gingold@xxxxxxxx>]

[...]
> > > The following is what I notice now.
> > >
> > > - pgd_populate(), pud_populate(), pmd_populate()
> > >   What if two cpu try to populate same virtual address?
> > >   Given that page allocation on demand is now removed, it might be
> > > possible to all necessary pgd/pud/pmd/pte page is allocate at domain
> > > creation.
This could be easily fixed.  However there is also no lock in the current Xen, 
so I think the kernel never does that.

> > > - guest_physmap_add_page()
> > >     assign_domain_page_replace()
> > >       ptep_get_and_clear()
> > >                       <<<<<<<<<<<< what if another cpu does set_pte()
> > > here? set_pte()
> > >     set_gpfn_from_mfn()
We should create a ptep_get_and_replace.
Is it enough ?
Since kernel is not supposed to access to pages being replaced, this shouldn't 
happen, should it ?

> > > - memory ordering
> > >   set_pte() doesn't have any memory relase semantics.
> > >   And readers (i.e. *(pte)) doesn't have acquire semantics.
> > >   I guess some memory barrier is required.
> > >   (spin lock means memory barrier)
I have added mp().

Currently, on a tiger 4, Xen crashes during boot with 2 cpus.  I will 
investigate.  There may be other issues...

Tristan.


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